DE69938372T2 - Method and device for video coding - Google Patents

Description

The The present invention relates to a video encoder and a Video encoding methods. More specifically, the present invention relates to a video encoder and a video coding method, whereby picture frames by cyclic insertion an intraframe coded region in each of the picture frames become.

One Video codec (coder / decoder) has a problem that when error in bitstreams in communication channels and storage systems are mixed, image data is not decoded correctly can be whereby deterioration of image quality is caused. With transmission channels less Bitrate and wireless networks in particular occur bit errors and cell loss easy on. It is therefore required fault resistance to increase.

It There are some countermeasures across from Errors. One of the effective countermeasures is image frames by cyclic insertion into the picture frames of an image region in which intraframe coding is performed refresh. Such an image region can be independent of other frames are decoded and thus not by mistake impaired in bitstreams mixed in the other frames. Therefore, the use allows of the refresh method for cyclically inserting an intraframe coding image region in each of image frames to increase the error resistance.

When a refresh method is a method known as intrasection (intrasclice) is called. For example, switching with MPEG-2 video (ISO-IEC CD 13818-2) between an intraframe coding mode (intra mode) and an interframe coding mode (Inter mode) in units of 16 × 16 pixels (macroblock). Z. For example, an intrasection-based refresh method has been proposed, by the one of a frame consisting of vertical 30 macroblocks and horizontal 44 macroblocks a region consisting of two macroblock lines (macroblock lines) (vertical two macroblocks x horizontal 44 macroblocks) in which intra mode is encoded, the intraframe encoded region is shifted by two lines each frame and 15 frames one Make cycle.

In This intrasection scheme becomes when a search for the motion vector carried out which communicates with a macroblock that is in one Region over the intraframe-coded region of the current frame is present, which is to be coded, the search area of the previous frame, which serves as the frame of reference, restricted, and the search will not performed by the non-refreshed region.

Z. For example, the search for motion vectors for macroblocks in the current frame so limited, that of macroblocks in the previous frame macroblocks in corresponding locations to the intraframe coded region in the current frame is not included in the motion vector search region are. In the case of intrasection, in which the direction of refreshment from top to bottom, therefore all motion vectors, which are directed from bottom to top, restricted. such restrictions allow frames in the worst case by the (2 cycles - 1) th frame from a frame in which errors have occurred, completely refreshed and allow the error propagation to converge.

Accepted z. For example, the cycle of intrasection is four frames and errors in the whole bit stream in the first frame in a cycle of four Framework have occurred. In this case, when coding a Macroblocks in an input frame in the Inter mode only Macroblocks the, of macroblocks in the frame of reference, exist in the same place as and the region over This macroblock to encode is in the input frame for the Motion vector search used. Thus, the area converges through the effects of errors spread to the lowest region in the frame.

The Number of coded bits in the intra mode is twice or more greater than in the inter-mode, if the same quantization parameters be used. Because there are restrictions in transfer rates It is necessary that the transmission rate of bitstreams on a certain value or less is limited. If that's on intrasection based refresh scheme is used, it is therefore necessary the number of coded bits by the amount corresponding to the intrasection, to insert is to reduce by adding quantization parameters greater than be made in the case where no intrasection is inserted. This however, is a serious cause of deterioration of image quality.

As in Japanese Unexamined Patent Publication No. Hei. 9-247682 By way of example, several adaptive refresh schemes have recently been proposed which adaptively refresh only regions in a scene that have a large amount of motion, thereby reducing the insertion number of intracoding regions. For motionless (silent) regions without motion, error concealment techniques can be used to embed corresponding regions in the previous frame into the current frame. By adaptive refresher only Thus, in regions that are large in motion, it becomes possible to effect reduction of information content while maintaining the fault resistance.

The usual Adaptive refresher schemes share a problem that movement that not to be considered intra-coded regions in a scene.

D. H. the conventional ones adopt adaptive refresh schemes the principle that once a region is refreshed by an intra-coded region is, she is not refreshed until a new move with that of this region. Thus, as soon as a region in which intra-mode is encoded, it clearly as one immobile regions considered in this point and from the refreshment area ruled out until a new movement with this region in Connection is detected.

For this reason, in the case that when a scene change occurs and the picture is unmoved after the scene change, intra-coded regions in the scene change frame fail because of errors during transmission to the decoder, error recovery is delayed, resulting in a serious problem. This will be in 11 illustrated.

In 11 It is assumed that a scene change occurs in a frame N + 1, and there is no movement for a while in regions of macroblock MBi in subsequent frames. In general, the switching between coding modes, such as the intra mode and the inter mode, is adaptively performed on a macroblock-by-macroblock basis in accordance with the degree of temporal correlation in an input video signal. If z. For example, as a scene change, a drastic change occurs in the picture, so that correlation between previous and current frames is completely lost, the intra mode is used. Thus, most of the macroblocks in the scene change frame N + 1 are encoded in the intra mode. When the conventional adaptive refresh type is performed from the top to the bottom in a four-frame cycle of frames N + 2, in frame N + 2, macroblock MBi is again to be refreshed, as shown. However, since the macroblock MBi is encoded in the previous frame N + 1 in the intra mode, the refresh of the macroblock MBi in the frame N + 2 is inevitably skipped. In this case, the inter mode is selected as the coding mode for the macroblock MBi in frame N + 2. However, since there is no motion, the non-coded mode is actually used, in which the corresponding macroblock in the previous frame is used for display without being coded.

After that MBi comes for a refresher in frame N + 6 again. Unless, it will move in macroblock MBi until then The macroblock refresh in frame N + 6 is also skipped.

Consequently is the macroblock MBi for not refreshed for a long time. If the macroblock MBi in the Scene change frame N + 1 due to transmission errors fails, can therefore correct information after a scene change for regions of the macroblock MBi are not preserved, so the image in the previous frame N before the scene change is displayed, like it is.

In literature EP 0485798A2 For example, a method and apparatus for refreshing motion-compensated sequential video images is described. Here, an image area is refreshed during transmission of a set of motion-compensated sequential video images. The video images are divided into a plurality of neighboring regions. The image area during a refresh cycle is refreshed by transmitting a different region in each successive video image of the set without moving the compensation. Motion compensation of the previously refreshed regions of the image area during the refresh cycle is limited to an area containing the previously refreshed region. Video image data from a current region being refreshed is encoded for use by the decoder in its identification as non-motion compensated data.

In literature EP 0712252A1 a motion picture encoding and decoding device will be described. This is described as a means capable of efficiently refreshing a picture and correcting picture deterioration caused by a coder in a short time. To do so, it is provided with a region shape measuring means which measures the shape of a motion compensation region by discriminating the motion compensation region from the other region in an image of a frame. It is also provided with a movement direction estimation means that estimates the moving direction based on the estimated starting point of the moving direction in the motion compensation region. A refresh operation is performed in the estimated moving direction from the starting point of the estimated moving direction in the motion compensation region. In the case where an error occurs in a block, a code error block number notification means notifies the block number and a refresh start point. The reference continues with a description that the Auf in either the estimated motion vector or in the estimated motion vector, but limited to those blocks containing or belonging to the motion compensation range. This allows those blocks in the static area not to undergo the refresh operation, allowing the refresh operation to be performed in a more efficient manner.

In literature USA 4827338 A hybrid encoding process by transformation, for the transmission of image signals, is described. Here, the images to be transmitted are defined by a sequence of frames, each frame containing a set of blocks organized in a matrix, each block containing a set of digital data organized in matrix form and forming part of the image , The process includes the steps of transforming each block in the frequency domain, quantizing the transformed coefficient of each block, evaluating the data volume necessary for encoding the transformed block by intra-frame statistical coding, evaluating the data volume if for encoding the transformed block necessary by statistical coding in interframe mode, comparing the data volumes and deciding the coding mode. The description goes on to talk about a decision unit deciding the coding mode for each block depending on signals from the processing means and the motion detection means. It also controls the addressing of a memory, and can avoid refreshing currently transformed blocks that already contain the memory. The motion detection means is of a conventional nature, wherein only the block is analyzed for differences between the current transformed block and the corresponding block of the previous frame.

As described above requires the conventional Intraschnitt based Refresh scheme, which considerably increases the amount of coding, quantization parameter big too to achieve coding at the same rate, where the picture quality deteriorated.

In addition, will with the adaptive refresh schemes to only motion regions refresh, as no refresh for a while after a scene change carried out error recovery is delayed in the event that errors in the scene change frame are mixed, the quality of a displayed image is degraded.

If the motion vector search area is restricted to error recovery Can ensure refresher furthermore, correct motion vectors are not dependent on image motion are found, whereby the image quality deteriorates.

It is an object of the present invention, a video encoder and to provide a video encoding method that allows the effects of transmission errors attenuated and thereby the image quality is improved, without increasing the Scope of coding.

According to one Aspect of the present invention, a video encoder is provided, comprising: coding means for selectively performing a Intraframe coding mode for Intra-frame coding of an input video signal, an inter-coding mode for interframe coding and a non-coded mode in which no coding is performed and the previous frame for an ad is used; Mode selection means for adaptively selecting one Encoding mode among the encoding modes for each predetermined region in the input video signal; and wherein the coding agent ent holds Intraframe coding means for Intraframing coding of regions to be refreshed by a Refreshment determining means are determined, characterized by Refresh control means for detecting a movement region of within a frame and setting up an intraframe-coded one Region for a refreshment in a section of a refreshment area in the next Frame containing the motion region, wherein the refresh control means contains Determining means for determining whether each of the intraframe-coded ones Regions coded by the coding means in the intraframe coding mode in the previous frame, to a motion region or a silent region heard, and the refresh determination means responds to a determination the determining means for inclusion of intraframe-coded Regions leading to the motion region in the refresh area belong, and exclusion of intraframe encoded regions belonging to the breastfeeding region the refresh area, and the coding means means for cyclic Insert of the intraframe coded regions in each of image frames according to a predetermined refresh cycle period.

This video encoder requires an adaptive refresh scheme that selects only a motion region within a frame as a refresh area and inserts an intra-coded region into a portion of the refresh area. Ie. a still region is excluded from the refresh area. Thus, in comparison with the normal intrasection, since the unmoved region is not refreshed, the number of Reduces macroblocks to be encoded in the intra mode, and at the same rate, the quantization parameters can be made correspondingly small, which helps to improve the picture quality.

at Determination of the refresh area is further, unlike the conventional one Refresh, the movement of the intra-coded region in the frame considered.

D. H. there will be an investigation of the degree of correlation between each of image regions encoded in the intra-mode, and the corresponding image region in the previous frame, and a determination is made of which of a motion region with motion and a still region without motion the image region belongs. Based on the result of this determination, the refresh area becomes certainly. In this case, the intra-coded region that belongs to belongs to the region of motion, added to the refresh area in the next frame, and the intra-coded region belonging to the non-moving region becomes excluded from the refresh area in the next frame, so that error recovery is done by refreshing can, even if the intra-coded region leading to the motor region belongs, through mistakes during a transfer to the encoder fails. By dynamically changing the Refreshing area on a base picture region for picture region according to the presence or lack of movement of the intra-coded region in the previous one Frame is thus continued, an intra-coded image region if it is a motion region to select as the refresh area until you later again intra-coded and is considered to belong to a still region. Consequently will be in such situations as there is a scene change frame and the image is motionless after the scene change, an intra-coded one Macroblock handled in the scene change frame as a motion region and refreshed at a predetermined time by the Refreshment area is determined. Even if an intra-macroblock in the scene change frame during transmission to the decoder fails, Therefore, error recovery can be based on refreshing relatively early carried out become.

The The present invention further provides a video encoder if the intra-frame coded regions are more than a predetermined number, that belong to the direction of movement, are included in a frame that determines refresh control means, that the frame is a scene change frame and changes in that next frame the place where an intraframe-coded region for a refresher is set up to perform the cyclic refresh operation in one End of the next Frame to begin.

Generally contains the scene change frame a large amount of coding, and therefore there is a high probability of mistakes being interfered with are, provided that the probability of occurrence an error unchanged remains. If errors are mixed in, there can be correlation between current and previous frame is lost, a technique like Error concealment, not used. By identifying a Scene change and start a refresh operation in one The end of the frame will be, even if errors in the scene change Frame occur, possible, worst case errors in a refresh cycle restore a predetermined number of frames.

It also puts the present invention provides a video encoder, wherein when one region in the next Frames that are in the same place as the intraframe encoded Region for a refresh in the previous frame is in the intercoding mode to be encoded, the refresh control means is a blocking means for Lock a motion vector search only for motion vectors from a movement region in the previous frame provided by the refresh control means is determined contains, where the motion vectors are in motion vectors in the direction are included opposite to the direction of the refreshment.

Around To ensure error recovery in (2 cycles - 1) painting locks as described above, the conventional Intraschnittschema the search for motion vectors in the opposite direction to the direction of refreshment completely. At the unmoved region is there a small possibility that mistakes are mixed. By removing the unmoved region the motion vector search area thus becomes the motion vector search area concentrated, which causes an improvement in image quality.

These Summary of the invention does not necessarily describe All the necessary features, so that the invention also a sub-combination this described features can be.

The The invention may be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

1 Fig. 10 is a block diagram of a video encoder according to a first embodiment of the present invention;

2 a flowchart for the encoding process in the video encoder of 1 is;

3 Fig. 10 is a schematic illustration of a refresh operation using horizontal macroblock lines;

4 Fig. 12 is a schematic illustration of a refresh operation using vertical macroblock lines;

5 Fig. 12 is a schematic representation of a refresh operation in units of a fixed number of macroblocks;

6 a diagram for use in explaining the refresh operation of the video encoder of 1 is;

7 a diagram for use in explaining the refresh operation of the video encoder of 1 is when there is a scene change;

8th a diagram for use in explaining restrictions in the motion vector search area in the video encoder of 1 is;

9 is a schematic representation of a radio communication system to which the present invention is applied;

10 an example of an operation form of the radio communication system of 9 is; and

11 Figure 12 is a diagram for use in explaining the operation of a conventional adaptive refresh scheme.

In 1 becomes an input video signal in macroblocks in a blocking circuit 11 divided. The input video signal divided into macroblocks enters a subtractor 12 where the input video signal and a prediction video signal to be described later are subtracted and their difference provides a predictive test error signal. One of both the predictive test signal and the input video signal from the blocking circuit 11 is controlled by a mode selector switch 13 and then discrete cosine transform in a DCT circuit 14 subjected. DCT coefficient data used in the DCT circuit 14 are obtained in a quantization circuit 15 quantized. The output of the quantization circuit 15 is divided into two; one is in a variable length coder 25 encoded according to variable length.

The other of the shared outputs of the quantization circuit 15 is in a dequantization circuit 16 and reverse DCT (IDCT) circuitry 17 dequantized in a sequence and DCT encoded, and then in an adder 18 to a prediction image signal from a switch 21 is added, thereby generating a local decoded signal. The local decoded signal is stored in a frame memory 19 stored and then into a motion compensation circuit 20 fed. The motion compensation circuit performs the motion compensation process, such as motion detection and motion vector search, based on correlation between the input video signal and the video signal in the previous frame stored in the frame memory 19 , thereby generating the prediction video signal and necessary information to a mode selector 22 and a refresh determination circuit 23 is sent.

A coding control circuit 24 , which is used for rate control, controls coding based on coded information from an encoder section 28 and the buffer amount from an output buffer 17 and sends necessary information to the variable-length encoder circuit 25 , In the variable length encoder circuit 25 DCT coefficient information is encoded together with motion vector information and mode information MODE. Image data generated by the encoding becomes a multiplexer circuit 26 where they are combined with coded voice data and other coded data, and the resulting multiplexed signal is then transmitted as coded data (bitstream) over a transmission channel at the transmission rate stored in the output buffer 27 is smoothed, transmitted.

The mode selector circuit 22 performs adaptive selection between macroblocks for interframe coding and macroblocks for intraframe coding based on prediction information P from the motion compensation circuit 20 which indicates the degree of inter macroblock correlation.

For intraframe coding, the switch becomes 13 to a terminal A is switched by mode selection switch information M, and the switch 21 is switched to a terminal A by switch information S. For interframe coding, on the other hand, the switch 13 switched to port B, and the switch 21 is switched to port B.

Encoding modes include an intra-frame coding (INTRA) intra-frame coding mode, an inter-frame encoding INTER mode (INTER), and a non-coding mode (NOT_CODED), wherein corresponding macroblock information is stored in the preceding frame frame is used for an ad as it is. A selection is made adaptive under these coding modes on a macroblock by macroblock basis. Normally, the INTRA mode is selected in the case where there is no interframe correlation. If interframe correlation can be used for a prediction, the INTER mode is selected. If there is no change in an image and therefore coding is unnecessary, the NOT_CODED mode is selected.

When the refresh determination circuit 23 issuing an instruction to perform refresh, also selects the mode selection circuit 23 the INTRA mode.

The mode selection switching information MODE indicative of a coding mode provided by the mode selection circuit 22 is selected becomes the variable length coding circuit 25 and the refresh determination circuit 23 Posted. The refresh determination circuit makes a determination as to whether or not each macroblock is to be included in a refresh region based on the selected encoding mode indicated by the mode selection mode MODE and the presence or absence of motion in intraframe-coded macroblocks. Based on the result of this determination, it is determined whether refreshment is to be performed or not.

The is called the present embodiment sets the adaptive refresher scheme that only motion regions in each frame as a refresh area. at however, a determination of the refresh area will be different than in the conventional one adaptive refresh scheme, the movement of an image over frames in each intramacroblock encoded in the INTRA mode. In this case will be for an intramacroblock, for which is the determination that it belongs to a region of motion, its region included in the refresh area in the next frame so that the refresher will provide recovery from errors, even if the macroblock itself by mistake during a transmission to the decoder fails. An intramacroblock, for the determination is that he belongs to a stationary region, will excluded from the refresh area in the next frame. In this way, the refresh area becomes the next frame on a macroblock basis for Macroblock according to the presence or lack of movement of the image in each intramacroblock in changed dynamically from the previous frame.

2 Fig. 10 is a flowchart for the processing operation of the refresh determination circuit 23 which illustrates the operation of performing cyclic refresh by shifting the INTRA coding region from top to bottom in units of a horizontal macroblock line from frame to frame.

Here i and j provide addresses in the vertical and horizontal directions, respectively in the frame of a macroblock to be encoded. V_NMB and H_NMB represent the numbers of macroblocks in the vertical and horizontal direction in the frame. N is the count in a counter, which indicates a macroblock line of a refresh location.

A two-dimensional field D [i] [j] includes elements for managing refresh control information that indicates, for each macroblock, whether or not it belongs to a motion region that needs refresh, based on the history of motion region / silence region determinations for each macroblock , The refresh control information for a macroblock in which rewriting has been performed, namely a macroblock for which the determination is a movement region due to the presence of a picture change, is set to FALSE. The refresh ^{control information rmation} for a macroblock for which the determination is that there is no change in an image is set to TRUE.

The FALSE indicates that the corresponding macroblock is currently in use belongs to a movement region. Unless the FALSE is rewritten as TRUE, it will Macroblock in a specific frame, through the refresh cycle is determined, refreshed.

The counter SC included in the refresh determination circuit 23 is provided, the number of INTRA macroblocks for which the determination is motion region counts for the purpose of determining a scene change.

In front a start of coding is first the counter value N to the refresh point found initialized to 0 (step S101).

When next becomes the counter SC for initializes a scene change determination to 0 before an inputted one 1 frame is coded (step S102).

In Loop 1 and Loop 2, the refresh determination and the encoding process are performed for each macroblock in the frame. In loop 2 consisting of steps S104 to S114, processing in the same macroblock line in the horizontal direction is performed. By interleaving loop 2 within loop 1 consisting of steps S103 and S104, For example, the macroblock line which is an object of processing is shifted from top to bottom, thereby processing a frame in its entirety.

In Step S105, an inquiry is made as to whether fulfilled two conditions or not: (1) the remainder of the division of the refresh counter value N by the number of macroblocks in the vertical direction, V_NMB, is equal to address i of a macroblock, currently one Object of coding is; and (2) the value of the field is D [i] [j] FALSE. If the macroblock that is about to be encoded belongs to the macroblock line, which is to be refreshed, then N modulo V_NMB is equal to i, the address the macroblock that is about to code. In addition, if the field value D [i] [j] is FALSE, then it is decided that the macroblock, the is about to become encoded, belonging to a movement region that needs to be refreshed.

If N modulo V_NMB is equal to the address i of the macroblock which is in the Term is to be coded, and the field value D [i] [j] is FALSE, what indicates the need of refresher, then becomes so the refresh is determined and the coding mode information MODE is rewritten to the INTRA mode (step S106).

To the coding process (step S107) is a coding mode determination carried out (Step S108), and then the field D [i] [j] becomes a coding mode type updated.

If the MODE is INTRA, then to determine whether the macroblock is stationary, the sum (SAD) of absolute values of prediction residuals of the macroblock for which the motion vector is the motion compensation circuit 20 is (0, 0), compared with a threshold TH (step S109). Ie. a check is made as to what degree the macroblock coded in the INTRA mode is different from the macroblock of the same address in the previous frame. If SAD is greater than TH, the determination is that the image is in motion. In this case, the corresponding field value D [i] [j] is set to FALSE indicating the necessity of refresh (step S110), and the count in the scene change determination counter SC is incremented by one (step S111). On the other hand, if SAD is not larger than TH, it is determined that the macroblock is unmoved. In this case, the corresponding field value D [i] [j] is set to TRUE, indicating that there is no need for refreshing (step S112).

If the MODE INTER is, it is decided that there is a movement in the Macroblock and then the corresponding field value D [i] [j] set to FALSE indicating the need for refresh (Step S113).

If If MODE is NOT_CODED, field D [i] [j] will not be updated and the operation goes to the next Loop.

When a result, the field value D [i] [j] is only rewritten to TRUE, when a macroblock is refreshed in a stationary region. Ie. when it is determined that a macroblock is in the INTRA mode encoded belongs to a motion region, or if a macroblock is encoded in the INTER mode, the field value D [i] [j] becomes FALSE and it continues, the macroblock as a refresh area select until the macroblock is in the same place in the subsequent frame as the macroblock is re-encoded in the INTRA mode and it it is determined that he belongs to a non-moving region.

To the termination of loop 1 and loop 2, d. H. if coding for one Frame is completed, the counter value SC for a scene change determination with a threshold E (step S116). If SC> E, it is decided that the frame, for the encoding has been completed, not a scene change frame, in which a scene changes. In this case, the refresh line to advance one, (N + 1) is divided by V_NMB and the remainder is considered a new value set for N. (Step S117). On the other hand, if SC is not greater than E, it is decided to that the frame, for the encoding has been completed is a scene change frame. In this case, N is reset to 0 (Step S118), thereby allowing the refresh operation of at the top of the next one Frame is restarted.

In the encoding process (step S107), the motion compensation circuit blocks 20 Motion compensation from a motion region among non-refreshed regions in the frame of reference to produce a predictive picture signal.

In the above description, the refresh operation is performed based on horizontal macroblock lines as in FIG 3 shown. Alternatively, as in 4 shown, the refresh operation are performed based on vertical macroblock lines. In such a case, it is only required that the division of N by V_NMB in steps S105 and S117 be replaced by the division of N by H_NMB, or the number of macroblocks in the horizontal direction.

Ie. with vertical refresher will be in Step S105, determinations of (J: N mod H_NMB) and (D [i] [j]: FALSE) are made. In other words, a check is made as to whether the two conditions are both satisfied: (1) the remainder of the division of the refresh counter value, N, by the number of macroblocks in the horizontal direction, H_NMB, is equal to the address j of a macroblock; which is about to be coded; and (2) the corresponding field value D [i] [j] has been set to FALSE. If the macroblock that is about to be encoded belongs to a macroblock line that is to be refreshed, the remainder of the division of N by H_NMB will be equal to the address i of that macroblock. If the field value D [i] [j] is set to FALSE, it means that the macroblock belongs to a motion region that needs to be refreshed.

If in step S105, N mod H_NMB equal to the address j of the macroblock is about to be coded, and also the corresponding field value D [i] [j] indicates FALSE, thus becomes the coding mode information MODE to the INTRA mode rewritten so that a refresh operation is performed.

In the above example, the refresh is performed based on a horizontal line or a vertical line. Alternatively, the refresh may be performed in units of a prescribed number of macroblocks, as in 5 shown. In this case, in step S105, determinations are made on (i × V_NMB + j) / RN: N mod ((i × V_NMB + j) / RN) mod D [i] [j]: FALSE.

More specifically, the above refresh mode is performed every horizontal line or vertical line, but the refresh may be performed in units of a predetermined number (R × N) of macroblocks, as in FIG 5 shown. In this case, in step S105, ((i × V_NMB + j) / RN: N mod (V_NMB × H_NMB) / RN) and (D [i] [j]: FALSE) are determined. In other words, the value obtained by dividing the address (i × V_NMB + j) of the macroblock to be encoded by the predetermined number (R × N) indicates an order in which the region is to be refreshed. It is determined whether two conditions: one that a value is equal to the rest obtained by the value of the refresh counter N by the number ((V_NMB × H_NMB) / RN) of regions to be refreshed, and the other one, that the value of the field D [i] [j] is "FALSE" or not. If the macroblock to be currently encoded belongs to the macroblock which is to be refreshed, the value obtained by dividing the address (i × V_NMB + j) of the macroblock to be encoded by the predetermined number (RN) equal to the remainder obtained by dividing the value of the counter N by the number ((V_NMB × H_NMB) / RN) of regions to be refreshed within the frame. If the value of the field D [i] [j] is "FALSE", it is also determined that the corresponding macroblock to be encoded belongs to the motion region to be refreshed.

Therefore in step S106, if the value obtained by dividing the address (i × V_NMB + j) of the macroblock to be encoded by the predetermined one Number RN is equal to the remainder obtained by Divide the value of the counter N is the number ((V_NMB × H_NMB) / RN) of Regions to be refreshed within the framework, and the Value of the field D [i] [j] "FALSE" is what the need the refresh indicates that the refresh must be done, and then the coding mode information MODE becomes the INTRA mode rewritten.

As described above, it is determined in this embodiment whether a MacroBlock is based on whether it has been rewritten as a result of a change in a picture after it was refreshed last. In this point is the important thing to determine if an INTRA encoding macroblock including Macroblocks which was previously refreshed in which INTER mode is encoded, he NOT_CODED. If so, it may include the INTRA encoding macroblock to a stationary region. Even if it fails, the effects can be exploited by using of the corresponding macroblock in the immediately preceding one Frame as he is suppressed become. If not, the macroblock is in a motion region available. If it fails, Thus the effects become serious. If the macroblock is in a non-moving region exists and has not been rewritten, it needs to be refreshed.

6 shows a horizontal macroblock line refresh operation of a frame sequence. In this example, it is assumed that the cycle period of the refresh is four frames and the refresh operation is performed from top to bottom of the frame.

In 6 Then, to the INTRA macroblock MBi in a still region refreshed in frame N, NOT_CODED macroblocks belonging to a still region continue through four consecutive frames corresponding to the cycle of refresh. In this case, in frame N + 1, the corresponding field D [i] [j] is maintained TRUE, indicating that there is no need for refresh; thus the refresh of the macroblock MB1 in frame N + 1 is skipped. Since the INTRA macroblock Mni + 3 in a still region refreshed in frame N + 3, NOT_CODED macroblocks up to Rah If N + 6 are followed, macroblock MBi + 3 in frame N + 7 is similarly skipped. However, if the macroblock MBi + 3 is skipped in frame N + 7, since it is encoded in the INTER mode, it is refreshed in the next refresh cycle.

Therefore represents this embodiment Recovering mistakes in, in the worst case, one (2 cycles - 1) Number of frames for sure.

7 shows a refresh operation when there is a scene change.

If a scene change in frame N + 1 occurs, essentially all macroblocks encoded in frame N + 1 in the INTRA mode. In this case, since every INTRA macroblock is present in a motion region, the corresponding field value D [i] [j] is set to FALSE, reflecting the need a refresh. Even if the intra macroblocks in frame N + 1 due to errors during a transmission Failure of the decoder can thus restore error afterwards relatively early carried out become.

In the present embodiment as described above, when it is determined that a frame a scene change frame is, after it has been encoded, the refresh point to the initial value in the next one Reset frame so that the cyclic refresh is started up in the next frame. In the case of refreshment from top to bottom, therefore, the Refresh in the top macroblock line in frame N + 2 following the scene change frame N + 1 started.

Generally, the frame in which a scene change occurs involves a large amount of coding, and therefore has a high probability that an error is mixed in with the same probability of the occurrence of the error. In the case where errors are mixed, an effective technique such as occlusion can not be used because of the lack of correlation with the previous frame. In particular, if no scene change is considered, the refresh-based restoration in the worst case will take a (2 cycles - 1) number of frames. However, by starting refreshing from the top of the frame immediately after a scene change, as in this embodiment, worst case recovery can be performed in one cycle, as in FIG 7 even if the scene change frame contains errors.

8th Figure 11 shows a relationship between INTRA coding regions inserted by refresh and unmoved regions.

As described above, in a search for the motion vector associated with a macroblock in a region, limited 1 over an intra-coding region in the current frame N + 2, the conventional system blocks the search range from the previous frame N + 1 serving as the reference frame, and blocks motion compensation from the entire region 2 that has not been refreshed yet.

For the still region, however, there is little need to lock motion compensation since there is little possibility of errors being intermingled. In the present embodiment, therefore, in order to facilitate restrictions in the motion vector search area and thereby improve the picture quality, the motion vector search with respect to still areas (J1 in frame N, j2 in frame N + 1 and J3 in frame N + 2) in the region 2 allowed. This is implemented by the refresh determination circuit 23 is allowed, movement regions and stationary regions in the region 2 in the frame of reference using the field D [i] [j] and the motion compensation circuit 20 to instruct to block the search for only the motor regions. The direction of the refresh can not only be from top to bottom, but also from bottom to top or from left to right. In this case, it is necessary to block the search for moving vectors in the direction opposite to the direction of the refresh only motion vectors of regions considered as moving regions.

The first embodiment was written to the value TRUE as the update of the field D [i] [j], indicating that there is no need for a refresher as soon as a stagnant INTRA macroblock appears. The conditions can be stricter, such that if a stagnant INTRA macroblock n times (n> 1) appears, he can be considered to belong to a still region. In This case can, even if an INTRA macroblock in one place in n consecutive frame fails, Error recovery can be done by refreshing.

Even though the embodiment has been described in terms of coding on a framework basis, In addition, the present invention is equally applicable Coding applicable on a field basis.

When next becomes a second embodiment of the present invention described below.

9 shows a configuration of a radio communication system using the video encoder of the present invention. The radio communication system includes a video transmission system 120 and a video reconstruction system 130 , Image information is transmitted from the video transmission system to the video reconstruction system via a network 140 transferred that with a base station 141 is provided.

The video transmission system 120 includes a video signal input section 121 , an information source encoder section 122 with a robust processor section 123 , a transmission line encoder section 123 , a transmission line encoder section 124 and a radio section 125 , In the information source encoder section, motion compensation, discrete cosine transformation (DCT), quantization and so forth are performed. In the transmission line encoder section, error detection and correction processing are performed in coded data. The information source encoder section has the video encoder of 1 and the robust processor implements the refresh control functions described above.

The video reconstruction system 130 includes a radio section 131 , an information source decoder section 133 with a robust processor 134 and a video signal output section 135 , The information source decoder section is adapted to decode bitstreams generated by the video encoder of 1 to be obtained. The robust processor 134 has error concealment functions.

10 FIG. 12 shows a form of operation of the radio communication system according to the second embodiment. FIG. As shown, video information is under terminals 50 such as laptop computers 151 and desktop computers 152 , via a communications network 140 with base stations 141 . 142 and 143 transfer.

Image information taken by a camera 151a is captured as an image information input section contained in the laptop computer 151 installed is coded by the information coder built into the computer. The coded data output from the information source encoder section and other voice information and data are multiplexed together and then radio-transmitted from the radio section and an antenna 151b , which is built into the computer, transmit. The transmitted image information becomes the network 140 through one near the base stations 141 to 143 to the network 140 sent and then through the antenna 152a of the destination computer 152 received by a near the base stations. The received information is demultiplexed into the picture coding information, speech information and data. The picture coding information is coded by the information source decoder section built in the computer and then displayed on the display of the computer.

Image information taken by the camera 152b is encoded in the same manner as above using the information source encoder section. The coded information and other voice information and data are multiplexed together and then transmitted by radio from the antenna 152a transfer. The transmitted radio signal is transmitted through the antenna 151a through the net 140 receive. The received information is demultiplexed into the picture coding information and other language information and data. The picture coding information is decoded by the information source decoder section in the computer and then displayed on its display.

As described above according to the present Invention by implementing the adaptive refresh information for determining the refresh area based on a determination, whether an intra-coded image region is either a motion region or a still region, the effects of transmission errors without increasing the Scope of coding, thus allowing the picture quality to increase. By reset the refresh point to the starting point in the frame immediately Following a scene change frame may also cause early error recovery in the case of failure of the scene change frame due to transmission errors carried out become.

Claims (17)

A video encoder comprising: coding means ( 28 ) for selectively performing an intraframe coding mode for intraframe coding of an input video signal, an interframe coding inter coding mode and a non-coded mode wherein no coding is performed and the previous frame is used for display; Mode selection means ( 22 ) for adaptively selecting a coding mode among the coding modes for each predetermined region in the input video signal; and wherein the coding means includes intraframe coding means for intraframe coding of regions to be refreshed, determined by a freshness determination means, characterized by: refresh control means ( 23 ) for detecting a moving region from within a frame and setting up an intraframe-coded region for a refresh in a portion of a refreshing area in the next frame that the Wherein the refresh control means includes determining means for determining whether each of the intraframe-coded regions coded by the coding means in the intraframe coding mode in the previous frame belongs to a motion region or a silent region, and the refresh determination means responds to a determination of Determining means for including intraframe coded regions belonging to the moving region in the refreshing area and excluding from the refreshing area intraframe coded regions belonging to the silent region, and the coding means means for cyclically inserting the intraframe coded regions into each one of picture frames according to a predetermined refresh cycle period. A video encoder according to claim 1, wherein when the intra-frame coded regions are included in a frame over a predetermined number belonging to the motion region, the refresh control means (12) 23 ) determines that the frame is a scene change frame and in the next frame changes the position in which an intraframe-coded region is set for refresh to start the cyclic refresh operation in an end of the next frame. A video encoder according to claim 1, wherein said refresh control means ( 23 ) cyclically shifts the location in which the intraframe-coded region is set for refresh, for each frame. A video encoder according to claim 3, wherein said refresh control means ( 23 ) shifts the intraframe coded region in the vertical direction of a frame on a macroblock line basis for each frame. A video encoder according to claim 3, wherein said refresh control means ( 23 ) shifts the intraframe coded region in the horizontal direction of a frame on a macroblock line basis for each frame. A video encoder according to claim 3, wherein said refresh control means ( 23 ) shifts the intraframe coded region in the horizontal direction of a frame in units of a predetermined number of macroblocks for each frame. A video encoder according to claim 3, wherein when the intraframe-coded regions are included in a frame over a predetermined number belonging to a motion region, the refresh control means (14) 23 ) determines that the frame is a scene change frame and in the next frame changes the position in which the intraframe-coded region is set for refresh to start the cyclic refresh operation in an end of the next frame. A video encoder according to claim 3, wherein when a Region in the next Frame that is in the same place as the intraframe-coded one Region for a refresher in the previous framework in which intervening Mode, the refresh control means includes prevention means to prevent a motion vector search only for motion vectors from one Movement region in the previous frame provided by the refresh control means is determined, wherein the motion vectors in motion vectors in the direction opposite to the direction of a refreshment are included. A video encoder according to claim 1, wherein said refresh control means ( 23 ) is configured to determine that each of the inter-coded regions coded in the inter coding mode by the coding means is a motion region and to determine the refresh area containing each inter-coded region. A video encoder according to claim 1, wherein the encoder means includes a motion compensation circuit for detecting motion on a macroblock-by-macroblock basis from a correlation between current and previous frames to generate prediction information, and the mode selection circuit (10; 22 ) performs an adaptive selection between a macroblock to be coded in the inter coding mode and a macroblock to be coded in the intraframe coding mode on the basis of the prediction information indicating the degree of the correlation. A video coding method comprising the steps of: selectively coding an input video signal in an intraframe coding mode, an interframe coding mode and a non-coding mode, wherein no coding is performed and the previous frame is used for display; adaptively selecting one of the encoding modes for each image region in the input video signal; Detecting a motion region from within a frame; Setting up an intra-frame encoded region for refreshing in a portion of a refresh area in the next frame containing the motion region; Determining whether each of the intraframe coded regions coded in the intraframe coding mode in the previous frame belongs to a motion region or a silent region; Determining a refresh area in the next frame based on a determination of determining to include intra-frame-coded regions belonging to the moving region in the refresh area and excluding from the refresh area intra-frame-coded regions belonging to the silence region; Intra-frame coding of regions to be refreshed included in the refresh area in the next frame; and cyclically inserting the intraframe-coded regions into each of picture frames according to a predetermined refresh cycle period. A video encoding method according to claim 11, further comprising determining that the frame is a scene change frame and change in the next Frame the location where the intraframe-coded region is for a refresher is set up to perform the cyclic refresh operation in one End of the next Frame when the intra-frame coded regions are longer as a predetermined number belonging to the moving region in a frame are included. A video encoding method according to claim 11, further comprising shifting the location of the intraframe-coded region for one Refresher cyclical for every frame. A video encoding method according to claim 13, wherein the intraframe coded region in the vertical direction of a Frame is moved on a macroblock line basis for each frame. A video encoding method according to claim 13, further comprising determining that the frame is a scene change frame and change in the next Frame the location where the intraframe-coded region is for a refresher is set up to perform the cyclic refresh operation in one End of the next Frame when the intra-frame coded regions are longer as a predetermined number belonging to a movement region in a frame are included. A video encoding method according to claim 13, further comprising preventing motion vector search only for motion vectors from a motion region in the previous frame, when a region in the next Frame that is in the same place as the intraframe-coded one Region for a refresh in the previous frame in the intercoding mode to encode, where the motion vectors in motion vectors in the direction opposite to the direction of a refreshment are included. A video encoding method according to claim 11, wherein the refresh area determining step includes determining that each of interframe-coded regions is a motion region, and determining of the refresh area containing each of the interframe-coded regions contains.